AN-9750 Datasheet, PDF (1/13 Pages) Fairchild Semiconductor – High-Power Factor Flyback Converter for LED Driver with

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AN-9750
High-Power Factor Flyback Converter for LED Driver with
FL7732 PSR Controller
Introduction
This highly integrated PWM controller, FL7732, provides
several features to enhance the performance of low-power
flyback converters. The proprietary topology enables
simplified circuit design for LED lighting applications. By
using single-stage topology with primary-side regulation, a
LED lighting board can be implemented with few external
components and minimized cost, without requiring an input
bulk capacitor and feedback circuitry. To implement high
power factor and low THD, constant on-time control
utilizes an external capacitor connected at the COMI pins.
Precise constant-current control regulates accurate output
current across changes in input voltage and output voltage.
The operating frequency is proportionally changed by the
output voltage to guarantee DCM operation with higher
efficiency and simple design. FL7732 provides protection
functions such as open-LED, short-LED and over-
temperature protection. The current-limit level is
automatically reduced to minimize the output current and
protect external components in short-LED condition.
This application note presents practical design consideration
for an LED driver employing Fairchild Semiconductor
PWM PSR controller FL7732. It includes designing the
transformer, selecting the components, and implementing
constant current regulation. The step-by-step design
procedure helps engineers design a power supply. The
design procedure is verified through an experimental
prototype converter. Figure 1 shows the typical application
circuit of primary-side controlled flyback converter using
FL7732 created in the design example.
© 2011 Fairchild Semiconductor Corporation
Rev. 1.0.3 • 5/15/12
Figure 1. Typical Application Circuit
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